Illumination based on semiconductor light sources, such as light-emitting diodes (LEDs), offers an efficient and long-lived alternative to fluorescent, high-intensity discharge and traditional incandescent lamps. Many LED light sources employ high powered LEDs, which pose thermal management problems and other related problems. Another drawback with state of the art LED devices is a high initial cost.
Small semiconductor die including those with sizes of 300 μm or smaller present several benefits in applications such as broad area lighting, concentrator photovoltaics and electronics. Light emitting elements with a lateral dimension equal or greater than 300 μm may also be used when driven at low currents.
Most commonly available LED drivers and drive circuits are designed to power relatively small numbers of LEDs (eg: 5 to 10) at moderate to high levels of current (eg: 20 mA-1 A) with a low voltage DC or constant current source. The total LED power of these arrays is therefore typically only a few watts. These drive solutions are not appropriate for driving higher power arrays of LEDs, for example an array of hundreds or even thousands of low power micro-LEDs with a total LED power exceeding for example 10 watts. Micro-LEDs typically have the same forward voltage as a standard or high flux LED, but the current required to drive a micro-LED is much smaller. For example, the drive current for a micro-LED is of the order of 5 mA or less. Even employing the lowest cost “multi-LED” linear regulator drive circuits currently on the market, with up to eight outputs each of up to 20 mA at ˜24 VDC, would require hundreds of such circuits, which would be prohibitively expensive and not very efficient.
Other, more expensive, high efficiency, switching regulator type LED drivers available on the market can efficiently output much higher currents, at different voltages supporting a string of a few LEDs (eg: 24 VDC, 36 VDC, 75 VDC, etc), but since micro-LEDs require such low current, in order to use these high current drivers it would necessitate grouping hundreds of micro-LEDs in parallel which would lead to reliability issues, be overly large due to all the inductors, and still not be very cost effective. Therefore, in order to cheaply and reliably drive hundreds or thousands of micro-LEDs with minimal component count and space usage and high efficiency, a significantly different topology and circuit design is required. This topology and circuit design is well suited to efficiently drive any array of LEDs with a medium to high level of total LED power. In addition, it may be applied to driving arrays of other light emitting elements such as laser diodes, or other semiconductor devices.